Sparkplug Node identity belongs in the Auth service

[amrc-benmorrow]

After quite a bit of thought about situations (e.g. cmdesc) where we are trying to authenticate data received over MQTT, I have decided:

• A Sparkplug Node is a security principal.
• The Sparkplug address of the Node is another identity mapping to the principal UUID, alongside the Kerberos UPN.
• Sparkplug addresses of Nodes should live in the Auth service.

There is a partial implementation of this already in the JS client library, which looks up addresses from the ConfigDB. It needs replacing with an API on this service.